Limit switch assembly for power driven valves



June 20, 1967 H. B. CARR 3,326,238

LIMIT SWITCH ASSEMBLY FOR POWER DRIVEN VALVES Filed July 9, 1965 2 Sheets-Sheet 1 [NI/EN ran. 3/ By HUGH a. CA RR c145 fiwle A I fomeys June 20, 1967 RR 3,326,238

IMIT SWITCH ASSEMBLY FOR POWER DRIVEN VALVES Filed July 9, 1965 2 Sheets-Sheet i Ar rarneys United States Patent O 3,326,238 LIMIT SWITH ASSEMBLY FOR POWER DRIVEN VALVES Hugh B. Carr, Carnegie, Pa., assiguor to S. P. Kinney Engineers, Inc., Carnegie, Pa., a corporation of Pennsylvania Filed July 9, 1965, Ser. No. 470,696 2 Claims. (Cl. 137-62417) This invention is for a limit switch for use in connection with automatically controlled actuating devices.

While the invention is applicable to various devices having a shaft which is rotated by an electric motor through a limited are, it will be specifically described, by way of illustration, in connection with a hot blast valve used in stove changing equipment in blast furnace operations. These valves are disc type valves movable up and down across a valve port into and out of open and closed positions and are remotely or automatically controlled.

Limit switches have been used which utilize the up and down movement of the valve stem to operate the switches but it is difiicult to maintain them in accurate adjustment because in the severe environment of a hot blast valve the stems of hot blast valves are frequently designed to permit lateral movement of the valve stem for proper operation.

According to the present invention, the limit switch is operatively connected to be driven by a reversible shaft which drives the valve or other device in one dircetion or the other. In a typical installation a reversible motor operates through reduction gears to drive a worm which meshes with a worm gear on the valve stem, whereby the valve is raised and lowered.

The reduction gear also drives a dial plate on the exterior of the valve which indicates the valve positions, i.e., open or closed. The limit switch is provided with a shaft which is rotated by the movement of this dial plate so the shaft follows the valve stem movement precisely. In the embodiment shown, two cams are mounted loosely on the shaft and means are provided for adjusting and locking the cams in proper selected angular relation. Electric switches are located above the cams and are electrically connected to the drive motor. As the shaft rotates, it carries the cams into and out of operating engagement with the switches to enable and disable the reversible valve drive mechanism.

The cams are positioned that number of degrees of shaft rotation apart corresponding to a valve movement from full open to full closed or vice versa, so that the cam surfaces are alternately brought into engagement with the switches. The shaft of course rotates less than 360, or one revolution, as the valve is moved between full open and full closed positions.

The switches are electrically connected in series with at least one other switch which is separate from the limit switch, so that the limit switch and at least one other switch must be closed to actuate the valve drive, while either may be opened to deactuate the drive. Each switch actuated by a cam may have plural contacts to provide electrical signals to other parts of an electrically interlocked installation, e.g. an automatic stove changing system for a blast furnace installation.

An object of the invention is to provide a new and useful limit switch assembly.

Another object of the present invention is to provide a reliable limit switch assembly for mounting on a power driven valve for enabling and disabling the valve drive means.

Another object is to provide a limit switch assembly which can be easily adapted to a plurality of valve drive mechanisms.

These and other objects will be more apparent by reference to the following drawings, wherein:

FIG. 1 is a general View of a typical valve with which the limit switch assembly of the invention may be used;

FIG. 2 is an end elevation of the limit switch assembly with the cover member removed;

FIG. 3 is a side elevation taken along the line III--III of FIG. 2 and showing the relationship of the limit switch assembly to the valve drive mechanism;

FIG. 4 is a detail of one of the cam assemblies;

FIG. 5 is an end elevation taken along the line VV of FIG. 4; and

FIG. 6 is a partly diagrammatic, partly schematic illustration of the electrical-mechanical relation between the limit switch and the valve drive motor.

Referring to the drawings, FIG. 1 is a general view of a typical hot blast valve and operating mechanism, the details of which are described in US. Patent No. 3,11,585 to Kinney et al., issued Dec. 10, 1963 and assigned to the assignee of the present invention.

In FIG. 1, 10 is a reversible electric motor which drives a vertical worm 11 which in turn drives a worm gear 12 connected to a shaft 13 (FIG. 3). The rotation of the shaft 13 operates the crank 14 and linkage 15 to raise and lower the valve stem 16 to open or close the valve. The shaft 13 also rotates a dial 17 which gives a visual indication of the valve position. Handwheel 18 may be used to operate the valve in lieu of motor 10 through the same operating components. The limit switch assembly 19 of the invention is mounted over the face of the dial 17 but so as not to obstruct the visual indication presented by the dial.

Referring to FIGS. 2 and 3, the limit switch assembly 19 is shown in greater detail. The worm 11, here shown in the horizontal for convenience in illustration, meshes with the worm gear 12 to rotate the drive shaft 13 and dial 17. The limit switch assembly 19 comprises a housing 20 having a base member 21 mounted in spaced relation to the worm gear box 22 by the bolts 23, and a cover member 24 mounted on the base member by bolts 25. A shaft 26 extends through the wall of the base 21 outwardly into the housing and inwardly into the space between the housing and gear box 22. On the inner end of the shaft 26 there is mounted a bifurcated lever arm 27 engaging between its bifurcations a pin 28 mounted on the face of the dial plate whereby the shaft 26 is rotated as the dial plate is rotated. Preferably the play between the pin and lever arm should not exceed .001 inch. The shaft 26 rotates Within a sleeve bearing 29 and has an annular moisture seal 30 disposed around the shaft between the shaft and bearing.

There are two spaced vernier cam assemblies 31 adjustably mounted on the shaft 26. The spacer 32 and retaining ring 33 maintain the longitudinal spacing between the two assemblies. Each assembly 31 comprises a cam 34 and a cam adjusting block 35 and suitable adjusting screws. As best seen in FIGS. 4 and 5, the cam 34 is shaped like a question mark ('2) to provide an arcuate cam surface 34a of constant radius describing an arc of 90 between the points A and B for a purpose which is explained later. Mounted on the shaft adjacent the cam 34 there is a cam clamping block 35 having upper and lower fingers 36 and 37 extending parallel to the shaft confronting the cam on opposite sides of the shaft 26. There is a spring 38 between the upper finger 36 and the cam 34 connecting the latter to the clamping block 35. This block is split to form two pinch arms 39 (FIG. 2) which may be loosened or tightened by the lock screw 40 which is threaded through the two arms 39 to provide coarse adjustment of the cam position on the shaft. On the side of the shaft opposite the spring 38 there is an adjusting screw 41 threaded through the lower extension of cam 34 to abut against the lower finger 37. This screw provides a Vernier adjustment for the cam and operates against the spring 38. The lock nut 42 locks the adjusting screw 41 into position after the vernier adjustment is made.

As seen in FIGS. 2 and 3, there are two shelves 43 extending from the base 21 and disposed above and on both sides of the shaft 26. A bracket 44 is mounted on the shelves and extends parallel to the shaft above the cams 34. The bracket 44 has an aperture therethrough directly above the cams 34 and depending lugs 45 on either side of the aperture. A pivot arm or actuator 46 is pivotally mounted intermediate its ends between the lugs 45 in vertical alignment with the shaft 26. On each end of the actuator 46 there are cam follower rollers 47 which alternately engage the cams 34 when the shaft is sufiiciently rotated. Atop the bracket 44 are mounted suitable electrical switches 48 having snap or spring action contacts which are operable by the spring-loaded plungers 49. Each end of the actuator 46 has upward projections 50 which abut the underside of plate 51 when the cams 34 engage the rollers 47. The plate 51 carries the plungers 49 which operate the switches. One set of contacts is employed for each direction of valve travel. Each set of contacts may contain one normally closed pair which are opened to deactuate the drive mechanism and another normally open pair which are closed to generate a signal indicative of the valve position, however, the switch arrangement may be varied depending on the associated circuitry and other factors. A suitable aperture 52 is provided in one wall of the base 21 for admitting the necessary wiring for the switches.

Operation As the valve drive mechanism drives the valve to an open or closed position, the worm gear 12, which is the last gear in the reduction gear train intermediate the motor and shaft 13, drives the dial plate carrying the pin 28 and lever arm 27 to rotate the shaft 26, causing one-or the other of the cams 34 to move into engagement with one of the rollers 47 whence one of the switches is operated to deactuate the valve drive means when the valve has reached its predetermined limits of travel. When the cam 34 is rotated out of contact with the actuator, the latter is returned to a neutral or horizontal position by the spring action of the switch plungers 49. The pivotally mounted actuator thus provides a mechanical interlock which prevents simultaneous actuation of both switches. The drive means will remain deactuated pending receipt of a further signal to again actuate the drive means for rotating the shaft 26 in a direction opposite the direction it was moving before the last deactuation. As shown in FIG. 6, the associated circuitry is such that once the valve drive has been stopped by the actuation of one of the switches 48, the drive means can then be made non-responsive to the position of that switch until completion of the next valve cycle by the opening of another switch in series.

As shown in FIG. 6, the reversible motor 10 is supplied with electric power through leads 53 and 54 and rotates the two cam assemblies 31 through the mechanical connections previously described and indicated by the numeral 55. Lead 54 divides into two branches 54a and 54b and into eachof these branches there is inserted, in series, a spring loaded limit switch 48 operated by a cam assembly 31 and a switch 56. Each of the switches 56 may represent the summation of a plurality of switches in an interlocked system and normally will be operated so that one is open when the other is closed and vice versa, as will beunderstood by those skilled in the art. This is so because the closure of either branch line 54a or 54b-will actuate the motor 10, there being one branch line for each direction of travel. Since both limit switches 48 will be closed by spring action when the valve is in a 4 position intermediate full open and full closed, only one of the summation switches 56 will be closed.

Since the cam surfaces 34a must be less than 360 of shaft rotation apart, the assembly may be used with any valve drive in which the shaft 26 has an annular movement of less than 360.

Many valves have internal parts removable by operating a hand wheel or the like, so it is necessary to provide for overtravel of the shaft 26 to prevent re-energizing the valve drive mechanism while the hand wheel is used to raise the stem beyond its normal operating travel for access to the internal parts. For this purpose the cam surface allows for an overtravel of rotation of the shaft 26 when the valve is being powered by means other than the power means electrically connected to the switches 48. The over-travel on the cam surface holds the particular switch 48 open while the valve is moved beyond the full open position for example.

The cams are adjusted to proper operating position by first moving the valve to its full open or full closed position. Next, the proper cam is rotated on the shaft 26 into switch-operating engagement with one of the cam-follower rollers 47. The cam is then locked in that position by the screw 40 operating on the pinch arms 39. Fine adjustment may then be made with the adjusting screw 41.

When the adjusting screw is screwed against the lower finger 37 the upper finger 36 tends to compress the spring to rotate the cam in a clockwise direction as viewed in FIG. 5. Similarly, loosening of the adjusting screw, in

:a direction away from the lower finger 36, causes the upper finger to stretch the spring which reacts to rotate the cam in a counterclockwise direction. The valve is then moved to its opposite position and the other cam is similarly locked on the shaft 26 in switch-operating engagement with the other roller 47. In the illustrations, the cams are positioned 90 apart. The cams are physically spaced apart, but, as before explained, each cam surface provides for a 90 overtravel. Because the cams are rotated first in one direction then the other, the effective spacing between the cams is thus 90. In other words a valve movement from full open to full closed position, or vice versa, corresponds to a 90 rotation of the shaft 26. As will be understood by those skilled in the art, terms full open and full closed as used herein are terms of convenience and do not necessarily mean the absolute mechanical limits between which the valve might be moved, but may be a percentage of the full travel limits as determined by the user.

While one embodiment of the invention has been shown, it will be understood that variations and modifications in the construction and arrangement of parts may be made within the scope and spirit of the invention.

I claim:

1. In combination with a power driven valve having an operating stem serving to move the valve into and out of open and closed positions, a drive shaft connected to the stem for effecting stem movements, the drive shaft being rotatable through a limited arc of less than 360, and electrically controlled power means operatively connected to the drive shaft for effecting rotation thereof, the improvement comprising,

(a) a cam shaft connected to the drive shaft to rotate through the same number of degrees of are as the drive shaft,

(b) a pair of switch-actuating cams mounted on the cam shaft for rotation therewith, the cams being axially spaced on the cam shaft, each cam having a switch-engaging surface, each such surface being angularly spaced a predetermined number of degrees of arc apart corresponding to the drive shaft rotation necessary to move the valve stem from an open to a closed position, wherein each cam comprises:

(1) a first switch-actuating member mounted loosely on the cam shaft for selective angular positioning of the first member, and

(2') a second member cooperating with the cam shaft and the first member for holding the latter in a selected position, the second member having a pair of abutments extending generally parallel to the cam shaft toward the first member,

(c) spring means connecting the first member to one of the abutments on the second member,

(d) screw means mounted on the first member and screwable into abutting relation with the other of the abutments on the second member, whereby the angular position of the cam is adjustable by the screw means, and

(e) a pair of switches each mounted adjacent the cam shaft for operative engagement with a particular one of the cam switch-engaging surfaces, each switch being electrically connected to the power means such that the actuation of each switch by its corresponding cam is effective to deactuate the power means.

2. In combination with a power driven valve having an operating stem serving to move the valve into and out of open and closed positions, a drive shaft connected to the stem for effecting stem movements, the drive shaft being rotatable through a limited arc of less than 360, and electrically controlled power means operatively connected to the drive shaft for effecting rotation thereof, the improvement comprising,

(a) a cam shaft connected to the drive shaft to rotate through the same number of degrees of are as the drive shaft, the connection between the drive shaft and cam shaft comprising,

(1') an indicating dial plate mounted on the valve drive shaft for rotation therewith,

(2) a pin extending from the dial plate, and

(3) an arm mounted on the cam shaft and having one end thereof bifurcated, the pin being disposed between the bifurcations,

(b) a pair of switch-actuating cams mounted on the cam shaft for rotation therewith, the cams being axially spaced on the cam shaft, each cam having a switch-engaging surface, each such surface being angularly spaced a predetermined number of degrees of arc apart corresponding to the drive shaft rotation necessary to move the valve stem from an open to a closed position, and

(c) a pair of switches each mounted adjacent the cam shaft for operative engagement with a particular one of the cam switch-engaging surfaces, each switch being electrically connected to the power means such that the actuation of each switch by its corresponding cam is effective to deactuate the power means.

References Cited UNITED STATES PATENTS 2,571,818 10/1951 Blodgett 200-47 2,747,056 5/1956 Jefferson 200153 2,953,656 9/1960 Bastes 200-67 FOREIGN PATENTS 990,113 5/1951 France. 1,160,924 1/ 1964 Germany.

BERNARD A. GILHEANY, Primary Examiner.

H. E. SPRINGBORN, Assistant Examiner. 

1. IN COMBINATION WITH A POWER DRIVEN VALVE HAVING AN OPERATING STEM SERVING TO MOVE THE VALVE INTO AND OUT OF OPEN AND CLOSED POSITIONS, A DRIVE SHAFT CONNECTED TO THE STEM FOR EFFECTING STEM MOVEMENTS, THE DRIVE SHAFT BEING ROTATABLE THROUGH A LIMITED ARC OF LESS THAN 360*, AND ELECTRICALLY CONTROLLED POWER MEANS OPERATIVELY CONNECTED TO THE DRIVE SHAFT FOR EFFECTING ROTATION THEREOF, THE IMPROVEMENT COMPRISING, (A) A CAM SHAFT CONNECTED TO THE DRIVE SHAFT TO ROTATE THROUGH THE SAME NUMBER OF DEGREES OF ARC AS THE DRIVE SHAFT, (B) A PAIR OF SWITCH-ACTUATING CAMS MOUNTED ON THE CAM SHAFT FOR ROTATION THEREWITH, THE CAMS BEING AXIALLY SPACED ON THE CAM SHAFT, EACH CAM HAVING A SWITCH-ENGAGING SURFACE, EACH SUCH SURFACE BEING ANGULARLY SPACED A PREDETERMINED NUMBER OF DEGREES OF ARC APART CORRESPONDING TO THE DRIVE SHAFT ROTATION NECESSARY TO MOVE THE VALVE STEM FROM AN OPEN TO A CLOSED POSITION, WHEREIN EACH CAM COMPRISES: 